Recursive integrator

ABSTRACT

An apparatus and method for weighting new and stored radar information. For each hit (or detected noise pulse), a quantizer sends a digital signal to a corresponding storage bin. The information from the current signal and respective previous signals is accumulated, recorded in a memory circuit for future retrieval and sent to a detection circuit which provides an output. After a predetermined number of hits the accumulation is divided by two, thereby effectively reducing the influence of previous signals while retaining their significance.

United States Patent [151 3,680,088 Bryant et al. 51 July 25, 1972 [54] RECURSIVE INTEGRATOR 3,353,177 11/1967 Wilmot ..343/5 DP 3,422,435 1/1969 Cragon et a1. ..343/5 DP [72] Inventors: Kenneth Owen Bryant, Ridgecrest; William R. Morrow, Inyokern; Vernon J. Logue, Ridgecrest, all of Calif.

Primary Examiner-Malcolm F. l-lubler Attorney-R. S. Sciascia and Roy Miller [73] Assignee: The United States of America as 57 BSTRACT represented by the Secretary of the Navy 1 A An apparatus and method for weighting new and stored radar [22] March 1970 information. For each hit (or detected noise pulse), a quan- [21] APPL NoI 23,645 tizer sends a digital signal to a corresponding storage bin. The information from the current signal and respective previous signals is accumulated, recorded in a memory circuit for fu- [52] [1.8. CI. ..343/5 DP ture retrieval and sent to a detection circuit which provides an [51] Int. Cl ..G01s 9/02 output. After a predetermined number of hits the accumu1a- [58] Field of Search ..343/5 DP tion is divided by two, thereby elfectively reducing the influence of previous signals while retaining their significance. [56] References Cited UNITED STATES PATENTS 6 Claim, 2 Drawing figures 3,206,747 9/1965 Caspers ..343/5 DP lfilfiilfi a l0 l2 l4 saws: 23 24 25 20 V I6 22 28 mvm: DETECTION 4 'NTEGRATED CIRCUIT ACCUMULATOR CIRCUIT lYlgggEglllgrpuT MEMORY JuLzsmz 3.680.088

ROY MILLER ATTORNEY RECURSIVE INTEGRATOR GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore.

BACKGROUND OF THE INVENTION In the field of radar target detection, one of the major problems has been in improving the probability of detection, particularly for a low signal to noise ratio situation. Prior devices utilize reset integrators in which all of the stored data is reset to zero after a selected number of radar interpulse periods. With such a device, when the target appears at the moment in which the stored data is reset to zero the probability of detection is relatively high. If the target appears at any other time, however, and the expected hits on the target equals the number of samples in any integration period, the probability of detection is relatively low since the accumulated integrated information output will often fail to reach the threshold detection level.

The present invention improves the probability of target detection by dividing the past accumulated integrated information by two at the end of an integration period rather than resetting all the stored data to zero. By utilizing the invention, a target appearing midway through the integration period N and being present N pulse periods, (the case of lowest probability of detection for the reset integrator), will probably be detected since the accumulated integrated information output will likely exceed the threshold detection level.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the invention; and FIG. 2 is a block diagram of the invention in greater detail.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 the recursive integrator comprises a rotating antenna 6, a radar system 8, an envelope detector 10, a quantizer 12, a shift register 14, an accumulator 16, a memory 18, a divide circuit 20, and a detection circuit 22, providing an integrated synthetic video output 26.

A return signal from the target is received by the rotating antenna 6 and adapted by radar system 8 to provide an intermediate frequency output plus noise 23. The envelope detector 10 receives the IF signal plus noise 23 as an input and provides a unipolar video signal 24 as an output. The quantizer l2 converts the unipolar video output 24 into a binary video signal 25 which is supplied to the shift register 14. The information in the binary video signal 25 is in the form of binary digits, called bits.

After receiving a predetermined number of bits the shift register 14 transfers the information contained therein to the accumulator 16. The shift register then receives the next interval period of additional bits, called a cell.

In the accumulator 16, information from the previous corresponding cells, supplied by memory 18 is added to the current cell sample. The output is compared to a predetermined threshold level in the detection circuit 22, which provides the system output 26.

After a predetermined number of interpulse periods the divide circuit 20 is activated and effectively divides the accumulated integrator output from accumulator 16 by a factor of two. The divide register 20 is activated only once every N interpulse periods where N is the integration time.

Referring now to FIG. 2 wherein the shift register 14, the accumulator 16, the divide circuit 20 and the detection circuit 22 are shown in greater detail. By way of example, shift register 14 has six information bins which are consecutively filled by bits of the binary video signal 25. After each six sample bits, the bits are transferred in parallel to bins 50 60 where they are held for accumulation in respective registers 70 of the accumulator 16. The shift register 14 will continue shifting to receive the next following-six samples of binary video. A 3 megacycle clockpulse 28 is used to provide an appropriate timing system to the device.

Each register 70 80 is a seven-bit binary accumulator capable of counting to 2 l, or 127. Summed values of respective samples of prior interval-periods, called ensembles, are transferred from memory 18 to the corresponding bin accumulators and added to the respective current bits. As an example, prior bits from bin 50 are stored in memory 18 for use in register 70. The resulting ensemble values are transferred serially to detection circuit 22 and, in parallel, tomemory 18.

In the detection circuit 22 each ensemble is evaluated by a predetermined criterion, threshold 105. For each ensemble in comparators that exceeds the criterion, a digital ONE. is produced, but for each ensemble that is less than the criterion, a digital ZERO is produced. The resulting integrated synthetic video output .26 is displayed on a monitor and transferred to a target evaluation circuit.

An an example of the operation of the accumulator 16, memory 18, and divide registers 20, the following discussion will be in reference to 'bin 50, seven-bit register 70, and the respective memory 18 and divide circuit 20.

An information bit value transferred from shift register 14 is stored in bin 50 even as shift register l4is shifted to receive new information bits. The bit value in bin 50 is added to the accumulated bit value in seven-bit register 70. Register 70 is a binary digit counter wherein a ONE in bit l40signifies a value of 64. The resultant value is simultaneously sent to detection circuit 22 and stored in memory 18 for future accumulations.

After a predetermined number of interpulse periods in which bit values in bin 50 are added to the accumulated values in seven-bit register 70, divide circuit 20 effectively divides the sum by two by shifting the binary digit counter in seven-bit register 70 one position toward the least significant bit. For example, if the accumulated value is 32 at the time of the division, that is, a one in cell 142 followed by five zeroes in cells 144 152, the accumulated value is divided by two by shifting the binary digit ONE from cell 142 to 144. A ONE in cell 144 denotes a value of l6.

The advantages of the invention are a reduced component count, and thereby a reduced cost of production, over most integrating devices, and the utilization of all information bits with the most recent being given greater influence. By dividing the accumulated integrated information by two rather than resetting the stored information to zero the system retains the previous information but reduces its influence, improves the signal to noise ratio, and increases the probability of target detection.

What is claimed is:

l. A video pulse processor for receiving radar echo pulses and preparing said pulses for display and input to a target evaluation circuit comprising:

abinary digit providing means for receiving said echo pulses as an input and providing said pulse information in the form of binary digits as an output,

means for receiving and storing the information from previous and currentpulses, including means for providing as an output the information stored,

means for accumulating the outputs of said binary digit providing means and said receiving and storing means and providing the accumulation as an output,

means for weighting the accumulated information from said binary digit providing means and said receiving and storing means so that the information from said binary digit providing means will be more significant in the output of said pulse video processor than any single previous pulse, including means for periodically reducing said accumulated output to a value other than zero, and

means for receiving said weighted accumulated outputs and providing an output of information suitable for use by a target evaluation circuit.

2. The processor of claim I wherein said reducing means periodically divides the accumulated output by two.

3. The processor of claim 2 wherein said reducing means is more significant to said accumulated information than shifts said accumulator one binary digit cell to accomplish said any single previous pulse, division. storing said weighted accumulated information for use in fu- A method of Video processmfi raqar E P ture accumulation as said previous echo pulses, and p y q p q i e? evaluatlpp conypnsmg; 5 outputting said weighted accumulated information in a form recewmg Sal cc P 565 contammg m ormauoni suitable for use by a target evaluation circuit. cotnvertmg said pulse information rnto binary drgrt mforma- The method of claim 4 wherein said weighting step prises; 3:233:25 l gg g g mformanon from prevlous l 0 periodically dividing the accumulated information by two. weighting said accumulated information by periodically g ig g f clmm wherem gj i f mforreducing said accumulated information to a value other manoms M ytwo on y once every accumu auons' than zero so that the information from said current pulse 

1. A video pulse processor for receiving radar echo pulses and preparing said puLses for display and input to a target evaluation circuit comprising: a binary digit providing means for receiving said echo pulses as an input and providing said pulse information in the form of binary digits as an output, means for receiving and storing the information from previous and current pulses, including means for providing as an output the information stored, means for accumulating the outputs of said binary digit providing means and said receiving and storing means and providing the accumulation as an output, means for weighting the accumulated information from said binary digit providing means and said receiving and storing means so that the information from said binary digit providing means will be more significant in the output of said pulse video processor than any single previous pulse, including means for periodically reducing said accumulated output to a value other than zero, and means for receiving said weighted accumulated outputs and providing an output of information suitable for use by a target evaluation circuit.
 2. The processor of claim 1 wherein said reducing means periodically divides the accumulated output by two.
 3. The processor of claim 2 wherein said reducing means shifts said accumulator one binary digit cell to accomplish said division.
 4. A method of video processing radar echo pulses for display and output to a target evaluation circuit comprising; receiving said echo pulses containing information, converting said pulse information into binary digit information, accumulating said binary digit information from previous and current said echo pulses, weighting said accumulated information by periodically reducing said accumulated information to a value other than zero so that the information from said current pulse is more significant to said accumulated information than any single previous pulse, storing said weighted accumulated information for use in future accumulation as said previous echo pulses, and outputting said weighted accumulated information in a form suitable for use by a target evaluation circuit.
 5. The method of claim 4 wherein said weighting step comprises; periodically dividing the accumulated information by two.
 6. The method of claim 5 wherein said accumulated information is divided by two only once every 64 accumulations. 